Conventionally, a glass substrate for an information recording medium must have a surface that is as smooth as possible to enable recording of information with high density. Thus, the surface of the glass substrate is ground and polished in plural stages during manufacturing to suppress the formation of microscopic protuberances (refer to, for example, Japanese Laid-Open Patent Publication No. 11-154325). That is, the glass substrate is ground and polished in steps divided into rough grinding, fine grinding, first polishing, and second polishing (final polishing).
The first polishing is a step using a polishing device to polish the surface of the glass substrate with a hard polisher until the surface roughness Rmax thereof is about 10 nm. The second polishing is a step using the same polishing device as the first polishing step to polish the surface of the glass substrate with a soft polisher in place of the hard polisher. For the polishing agent of the first polishing and the second polishing, cerium oxide, zirconium oxide, and colloidal silica and the like containing particles of and silicon oxide is selected and used in accordance with the required polishing accuracy or the like.
Recent glass substrates are required to be recordable with higher density. To fulfill this requirement, the smoothness of the glass substrate surface must be improved. In order to improve smoothness, polishing must not only be divided into two stages of first polishing and second polishing but must further be divided into more stages, such as a third stage and a fourth stage. However, as the steps related to polishing become divided into many steps, tasks that are troublesome and that require a long period of time increase. Such tasks include transferring the glass substrate between polishing devices and performing cleaning between the steps. This has a shortcoming in that the productivity and yield decrease.
The present invention focuses on the above problem of the prior art. It is an object of the present invention to provide a glass substrate for an information recording medium that improves production efficiency and that increases the amount of production while maintaining quality, and a method for manufacturing the same.